replace qmake with cmake?

[aoloe]

i'm currently poriting the appimage creation for scribus from qt5 to qt6 and the process was / is not trivial.

one of the issue was that linuxdeployqt calls qmake but with qt6 the executable is qmake6.
(i'm now passing the path to qmake as an argument... but i had to find out about it, first...)

i'm still in the process of tweaking AppImage-package/bundle.sh but, when asking for help in the #qt channel, they suggested that for qt6 application it would be better to use cmake instead of qmake:

https://www.qt.io/blog/deploying-to-linux-with-cmake

[probonopd]

You can compile the application using cmake.

qmake/qmake6 is only needed by linuxdeployqt to determine the path to Qt. (Can that path be gotten from cmake? How?)

[dfaure-kdab]

With Qt6 you can use the cmake variable "${QT6_INSTALL_PREFIX}"

Otherwise you can query qmake with Qt5 and qtpaths with Qt6, like this
https://invent.kde.org/frameworks/extra-cmake-modules/-/blob/master/modules/ECMQueryQt.cmake

[probonopd]

@aoloe if you run qtpaths on your system, would it give the correct Qt path? Maybe we could use that in linuxdeployqt then.